The disclosure relates to a hydraulic control arrangement for supplying pressure medium to two consumer groups.
To supply pressure medium to hydraulic consumers of mobile working appliances, such as, for example, excavators, tractors or dredger loaders, LS (load sensing) or throttle systems are often employed. In what are known as LS systems, the pump pressure is regulated as a function of the maximum load pressure of the consumers. So that the pressure medium volume flow to each consumer can be set independently of the load pressure, in what are known as LS control blocks each of the consumers is assigned an adjustable metering orifice and a pressure balance which keep the pressure medium volume flow constant independently of the load pressure. In what are known as LUDV systems, a subgroup of the LS systems, the pressure balance is acted upon in the closing direction by the maximum load pressure of all the consumers and in the opening direction by the pressure downstream of the metering orifice. In the event of undersaturation, in these LUDV systems the available volume flow is apportioned proportionally in the ratio of the opened metering orifice cross sections.
In LS systems, the pump delivery flow is therefore adapted to the respective requirements. In contrast to this, in a load pressure-dependent throttle system the pump always conveys the maximum possible or constant delivery rate. In this case, the pump may be designed as a fixed displacement or variable displacement pump. In these throttle controls, what are known as open-center control blocks are used, such as are described, for example, in data sheets RD 64 266 or RD 64 122 of Bosch Rexroth AG. These throttle control blocks have a multiplicity of directional valve elements which, in their basic position, route the pump volume flow via a bypass duct back to the tank with a low pressure loss. When a valve slide of a valve element is being adjusted, the connection to the assigned consumer is opened continuously while the pressure medium volume flow in the bypass duct is throttled, so that the pump pressure rises to the load pressure of the consumer.
When a plurality of consumers are activated via a throttle control block of this type, the volume flow to the individual consumers is apportioned as a function of the respective load pressure, the pressure medium preferably flowing to the consumer having the lowest load pressure. When a plurality of consumers are activated, in this case a pump pressure is set which corresponds approximately to the maximum load pressure of the consumers plus a predetermined pressure difference. The pump pressure therefore has to be throttled back correspondingly to actuate the consumer with the lowest load, and therefore considerable throttle losses arise.
As already mentioned, mobile working appliances, for example dredger loaders, are designed with control blocks of this type. A dredger loader has, for example, at its front a loading shovel and at its rear dredger equipment, so that the dredger loader combines the functions of a wheeled loader and those of a dredger. The front-side attachments and rear-side attachments are usually activated in each case via a control block, while for reasons of cost a throttle control block is often used for the dredger function and makes it possible at lower outlay to activate the attachment with relative sensitivity, but has the throttle losses mentioned.
A further problem is that the rear-side hydraulic consumers and the front-side hydraulic consumers are often operated at a different load pressure level, so that, in the case of a common pump, setting to the maximum load pressure is carried out and the load pressures to the other consumers have to be throttled back considerably.
DE 43 22 127 B4 discloses a hydraulic control engine with two control blocks, of which one is designed as an LS control block and a further control block is designed as a throttle control block with an open-center directional valve. Both the LS control block and the throttle control block are supplied with pressure medium from a common variable displacement pump which is activated as a function of the maximum load pressure of both control blocks, so that the pump pressure always lies above the maximum load pressure of the system by a predetermined pressure difference. In a basic position of the directional valve of the throttle control block, an LS control line branching off from a pump line carrying the pump pressure is relieved toward the tank via the open center of the directional valve, so that, by the directional valve being adjusted, the control oil volume flow is throttled and the control pressure communicated to the variable displacement pump rises correspondingly. The maximum control pressure at the throttle control block is limited via a pressure-limiting valve.
This solution basically has the same disadvantages as those explained above. When different consumer groups having a different load pressure level are activated, the variable displacement pump has to be regulated in terms of the maximum load pressure, and this high load pressure has to be throttled back at the control block having the lower load pressure level, the throttle losses being considerable.
By contrast, the object on which the disclosure is based is to provide a hydraulic control arrangement, by means of which two consumer groups with a different load level can be activated, along with reduced losses.